Non-woven webs for many end uses, including filtration media, have been manufactured for many years. Such structures can be made from bicomponent or core shell materials are disclosed in, for example, Wincklhofer et al., U.S. Pat. No. 3,616,160; Sanders, U.S. Pat. No. 3,639,195; Perrotta, U.S. Pat. No. 4,210,540; Gessner, U.S. Pat. No. 5,108,827; Nielsen et al., U.S. Pat. No. 5,167,764; Nielsen et al., U.S. Pat. No. 5,167,765; Powers et al., U.S. Pat. No. 5,580,459; Berger, U.S. Pat. No. 5,620,641; Hollingsworth et al., U.S. Pat. No. 6,146,436; Berger, U.S. Pat. No. 6,174,603; Dong, U.S. Pat. No. 6,251,224; Amsler, U.S. Pat. No. 6,267,252; Sorvari et al., U.S. Pat. No. 6,355,079; Hunter, U.S. Pat. No. 6,419,721; Cox et al., U.S. Pat. No. 6,419,839; Stokes et al., U.S. Pat. No. 6,528,439; Amsler, U.S. Pat. No. H2,086, U.S. Pat. No. 5,853,439; U.S. Pat. No. 6,171,355; U.S. Pat. No. 6,355,076; U.S. Pat. No. 6,143,049; U.S. Pat. No. 6,187,073; U.S. Pat. No. 6,290,739; and U.S. Pat. No. 6,540,801; U.S. Pat. No. 6,530,969; Chung et al., U.S. Pat. No. 6,743,273; Chung et al., U.S. Pat. No. 6,924,028; Chung et al., U.S. Pat. No. 6,955,775; Chung et al., U.S. Pat. No. 7,070,640; Chung et al., U.S. Pat. No. 7,090,715; and Chung et al., U.S. Patent Publication No. 2003/0106294. This application incorporates by reference U.S. Pat. No. 6,290,739, issued Sep. 18, 2001, and U.S. Pat. No. 6,143,049 issued Nov. 7, 2000. Such structures have been applied and made by both air laid and wet laid processing and have been used in fluid, both gaseous and air and aqueous and non-aqueous liquid filtration applications, with some degree of success.
Filter elements having pore size gradients are known in the prior art and are advantageous for particulate filtration where the filter otherwise can become clogged in the most upstream layers, thus shortening the lifetime of the filter. Varona, U.S. Pat. No. 5,679,042, discloses a filter having pore size gradient through a nonwoven web, wherein a thermoplastic nonwoven web is selectively contacted by a heating element so as to shrink the pores in selected areas. Alternatively, the filter element may have zones of different fibers such that each zone has an average set of fiber composition; the zones are exposed to heat that shrinks some fibers according to composition and denier, resulting in shrinking pore size and variable shrinkage depending on fiber composition in that zone. Amsler, U.S. Stat. Inv. Reg. No. H2086, discloses filter media for filtering particles from a liquid, wherein the filter is made with at least three layers of nonwovens: a first outer web of multicomponent fibers; a second outer web; and composite web of thermoplastic microfibers and 50% or more of a material such as pulp, polymeric staple fibers, particles, etc. The first (upstream) layer preferably has higher porosity, higher loft and is preferably constructed of crimped bicomponent spunbond fibers. Emig et al., U.S. Pat. No. 6,706,086, disclose a vacuum cleaner bag having a highly porous backing material ply and a filter material ply. The backing material is cellulose fibers and fusible fibers, that is wet laid or air laid and may also have glass fibers and/or synthetic fibers. There may be more than one backing material layer in the bag construction. The filter material is nonwoven that may be meltblown and may comprise nanofibers. The bag may have the layers loosely joined by a single seam.
Substantial prior art surrounding pore size gradients in filter elements is directed to heating, ventilating, or air conditioning (HVAC) applications. For example, Arnold et al., U.S. Pat. No. 6,649,547, disclose a nonwoven laminate suitable for use as a filter for HVAC applications. The laminate has a microfiber layer integrated with a high loft multicomponent spunbond layer on one side and a low-loft multicomponent spunbond fiber on the other side. Preferably, the layers are through-air bonded and electret treated. Pike et al., U.S. Pat. No. 5,721,180 disclose a laminate filter media for HVAC applications, where first layer is electret high loft, spunbond crimped fiber web of low density and a second layer is electret meltblown microfiber layer having at least one polyolefin. Cusick et al., U.S. Pat. Nos. 5,800,586; 5,948,344; and 5,993,501, disclose a pleated composite filter media having randomly oriented fibers for use in HVAC type applications, e.g. automobile cabin air filtration. One or more thin stiffening layers help the construction retain its pleated formation, but the stiffening layer may also aid in filtration of dirt from air. Preferably, the mean fiber diameter increases, and density decreases, over the thickness of the fibrous filtration layer. Schultink et al., U.S. Pat. Nos. 7,094,270; 6,372,004; and 6,183,536, disclose a multiple layer filter for HVAC type applications or vacuum cleaner bags. Layers of filter media are bonded together in a laminate. One embodiment has layers that by themselves are of such high porosity or are so flimsy they are useless by themselves. Some layers can have particles, etc. for filtering odors or toxins.
Another area of prior art surrounding filters with pore size gradients is in oily mist filtration. Johnson, U.S. Pat. No. 6,007,608 discloses a mist filter having at least three stages: prefilter, intermediate layer and last layer, all composed of polyester fibers. The intermediate layer is pleated. The prefilter purpose traps the bulk of high loadings of mist to prevent carryover by overloading of the pleated media. The multiple layers comprise a pore size gradient. Hunter, U.S. Pat. No. 6,419,721 discloses an oil mist filter for coalescing and draining oil. The filter is multiply layered, with at least a coalescing layer and a drainage layer. The layers are not bonded. The coalescing layer is made of microfibers; the draining layer is nonwoven material bonded by fusible fibers.
We have not found any filter elements that are suitable for use in heavy-duty engine filtration applications where very high levels of both solid and oily aerosol particulate are encountered. The prior art filters for e.g. diesel engines does not solve the problems presented by newer generation engines where the level of soot passed through the filter is much higher than engines of past generations.
Pressure-charged diesel engines generate “blow-by” gases, i.e., a flow of air-fuel mixture leaking past pistons from the combustion chambers. Such “blow-by gases” generally comprise a gas phase, for example air or combustion off gases, carrying therein: (a) hydrophobic fluid (e.g., oil including fuel aerosol) principally comprising 0.1-5.0 micron droplets (principally, by number); and, (b) carbon contaminant from combustion, typically comprising carbon particles, a majority of which are about 0.01 to 1.0 microns in size. Such “blow-by gases” are generally directed outwardly from the engine block, through a blow-by vent. Herein when the term “hydrophobic fluids” is used in reference to the entrained liquid aerosol in gas flow, the reference is to non-aqueous fluids, especially oils. Generally such materials are immiscible in water. Herein the term “gas” or variants thereof, used in connection with the carrier fluid, refers to air, combustion off gases, and other carrier gases for the aerosol. The gases may carry substantial amounts of other components. Such components may include, for example, copper, lead, silicone, aluminum, iron, chromium, sodium, molybdenum, tin, and other heavy metals.
Engines operating in such systems as trucks, farm machinery, boats, buses, and other systems generally comprising diesel engines, may have significant gas flows contaminated as described above. For example, flow rates can be about 2-50 cubic feet per minute (cfm), typically 5 to 10 cfm. In such an aerosol separator in for example a turbocharged diesel engine, air is taken to the engine through an air filter that cleans the air taken in from the atmosphere. A turbo pushes clean air into engine. The air undergoes compression and combustion by engaging with pistons and fuel. During the combustion process, the engine gives off blow-by gases.
In the past, diesel engine crankcase ventilation gases were directed into the atmosphere. New environmental restrictions in many countries now severely limit these emissions. One solution to handling this problem is to vent the valve cover to a filter element which collects the blow-by oil droplets generated in the engine from the cylinders and mist droplets generated by the action in the crank case and valve area. Blow-by is directed through the filter element, which traps the oily aerosols and allows the balance of the air stream to pass through. Collected oil then drains out of the element and back to the crankcase. The filtered air is directed upstream of the engine air compressor so that any oil that passes through the crankcase ventilation (CCV) filter element will be burned in the engine. Oil must be removed from this air to reduce or eliminate oil collection on the walls of the air cooler and to protect the various air sensors from fouling.
The life of the filter element is dependent on the amount of soot or other material that is collected and remains on the fibers in the filter media of the filter element. Typical engines have soot levels that are within the capabilities of the oil to remain in suspension (act like a liquid). However, recently diesel engines have been manufactured that generate excessive amounts of soot. One source of soot is the compressor which is driven by exhaust gas from the engine. A portion of this exhaust is directed into the lubrication oil (engine oil) and back to the crank case. Thus the exhaust gas, containing soot, is mixed with blow-by, substantially increasing the amount of soot in the blow-by. The soot collects on the fibers of the CCV filter element, eventually restricting flow. Due to the relatively small particle size of the soot, 0.01 to 0.1 microns, the soot tends to collects on the first few layers of a filter element. The life of the filter element is thereby severely reduced due to clogging of the first few layers of the filter media.
Aerosols in particular are challenging in filtration applications. The ability to achieve certain filtration attributes such as pore size, basis weight, thickness, permeability and efficiency are limited by the manufacturing techniques used to make the paper layers and by the components useful in such layers. Because aerosols may be as small as 1 nm diameter or as large as 1 mm (W. Hinds, Aerosol Technology: Properties, Behavior, and Measurement of Airborne Particles 8, 2nd ed., © 1999 J. Wiley & Sons), conventional technologies are not suitably flexible to effectively accommodate the range of particle sizes in which aerosols may be encountered in fluid streams.
Some examples of conventional commercially available filtration media for the separation of aerosols, such as are present in blow-by, from air are products available from the Porous Media Company of St. Paul, Minn.; Keltec Technolab of Twinsburg, Ohio; ProPure Filtration Company of Tapei, Taiwan; Finite® and Balston® filters made by the Parker Hannifin Corporation of Mayfield, Ohio; Fai Filtri s.r.l. of Pontirolo Nuovo, Italy; Mann+Hummel Group of Ludwigsburg, Germany; and PSI Global Ltd. of Bowburn Durham, United Kingdom. However, none of these media are suitable for use in diesel engines where very high soot and oily aerosol loading is encountered in CCV filtration applications.
Thus, a substantial need exists for filtration media, filter elements, and filtration methods that can be used for removing multiple particulate materials from fluid streams, and in particular air streams. There is a substantial need for a filtration media, element, and method capable of filtration of high levels of both solid and liquid aerosol particulates from an air stream. The invention provides such media, filtration structures and methods and provides a unique media or media layer combinations that achieve improved permeability and long filtration life.
The variables toward which improvements are desired generally concern the following: (a) size/efficiency concerns; that is, a desire for good efficiency of separation while at the same time avoidance of a requirement for a large separator system; (b) cost/efficiency; that is, a desire for good or high efficiency without the requirement of substantially expensive systems; (c) versatility; that is, development of systems that can be adapted for a wide variety of shapes, applications, and uses, without significant re-engineering; and, (d) cleanability/regeneratability; that is, development of systems which can be readily cleaned (or regenerated) if such becomes desired, after prolonged use.